The full-service fitness club, which operates 73 centers in major U.S. markets, London and Toronto, signed a 25-year, 32,000-square-foot lease, officials with SL Green said.

No brokers represented either side in the deal, a spokeswoman for SL Green said. A representative for Equinox didn’t respond to a request for comment.

The spokeswoman for SL Green didn’t disclose the asking rents at the property between Fifth and Madison Avenues. But Midtown retail sites, which encompass all available retail spaces in properties between 35th and 59th Streets, command an average asking rent of $198 per square foot, according to the latest retail rent report from the Real Estate Board of New York.

SL Green purchased 10 East 53rd Street, previously known as the HarperCollins Tower for the publishing company that SL Green’s website still lists as a major tenant, for $252.5 million in 2012, according to city property records.

Equinox recently opened its 35,000-square-foot fitness club at Brookfield Place, which represented its fourth fitness center south of Houston Street when they signed the lease in 2013. Equinox also owns Blink Fitness and acquired six fitness businesses in New York City, Boston, Miami, San Francisco and Washington D.C. this summer, according to a release on the company’s website.